1. Field of the Invention
The present invention relates to a mechanism for closing a hinged member, in particular a door, a gate, a window, etc., which mechanism comprises a resilient element for effecting closure of the hinged member and a hydraulic damper for damping the closing movement of said hinged member. The damper itself comprises a closed cylinder cavity within a cylinder barrel, a piston placed within said cylinder cavity so as to divide it into a first and a second side, and a damper shaft coupled to said piston.
2. Background
Door or gate closing mechanisms which comprise a combination of a resilient element and a hydraulic damper to effect automatic closure of the hinged closure member without slamming are well-known in the art. The hydraulic components are however delicate and usually badly suited for outdoors use. They are more particularly quite sensitive to temperature variations and are also often subject to leakage problems.
Examples of such door closing mechanisms were disclosed, for example in U.S. Pat. No. 4,825,503 and UK Patent Application GB 2 252 790. These door closing mechanisms comprise a hydraulic rotation damper which includes a rotating piston. These known rotation dampers do however present several drawbacks. Because the rotating piston has a travel of less than 360°, the rotation damper is directly coupled to the actuator output, without any multiplication stages. Since in this application it is important for the damper to be as compact and unobtrusive as possible, the area of the piston is necessarily limited. To achieve the required damping torques, comparatively high hydraulic pressures will thus be required. This makes it more difficult to prevent leaking, in particular through the damping adjustment valve, which is in fluid connection with the high-pressure side of the damper. In particular in outdoor applications, which, to prevent being substantially affected by temperature changes, normally use a hydraulic fluid of low, substantially constant viscosity (i.e. a viscostatic fluid), the low viscosity of the fluid often requires additional measures to prevent leaks. Although only very small amounts of hydraulic fluid may leak out of the damper, it is important to avoid even such small leaks since the damper should be maintenance free for a large number of years.
A further drawback is that it is difficult to achieve a good sealing contact between the rotating piston and the inner wall of the cylinder. In fact, the rotating piston is formed by a rotating vane which has a free edge engaging the inner wall of the cylinder. Manufacturing such a vane and rotatably mounting it into the cylinder so that it fits exactly against the inner side of the cylinder, is a quite complex operation. Consequently, the production of the damper is relatively expensive and since the rotating piston will usually not fit exactly against the inner wall of the cylinder the hydraulic fluid has to be sufficiently viscous to be able to produce the required high pressure. A drawback of such viscous fluids is that their viscosity is usually quite strongly dependent on the temperature so that the known dampers are not appropriate for outdoor applications.
The present invention therefore relates to a closing mechanism the hydraulic rotation damper of which does not comprise a rotating piston but instead a rotating damper shaft, the rotation of which is converted into a translation of the piston. The hydraulic rotation damper comprises more particularly a closed cylinder cavity which has a longitudinal axis and which is defined by a substantially cup-shaped cylinder barrel; a rotational damper shaft which extends through an opening in the cylinder barrel into the cylinder cavity and which is rotatable with respect to said cylinder barrel substantially around said longitudinal axis; a piston placed within said cylinder so as to divide the cylinder cavity into a first side above the piston and a second side below the piston, and said piston comprising: at least one helical thread in engagement with a corresponding thread on either the cylinder barrel or the damper shaft, and a rotation-preventing member in engagement with a guide on the other one of said damper shaft or cylinder barrel, so that a rotational motion of the shaft with respect to the cylinder barrel results in a translational motion of the piston along said longitudinal axis; and a one-way valve allowing fluid flow from said first side to said second side of the cylinder cavity when opening the hinged member.
Such a type of hydraulic damper has already been disclosed in Austrian Patent AT 393 004 B. The piston of this damper is provided with a one-way valve enabling a flow of hydraulic fluid from the first side of the cylinder cavity to the second side thereof when the hinged member is opened. When the hinged member is closed, however, the hydraulic fluid can only flow from the second (high pressure) side to the first side through the clearance between the piston and the wall of the cylinder cavity so that this closing movement is damped. A drawback of such a rotation damper is however that its damping torque is not adjustable.
In the rotation damper disclosed in U.S. Pat. No. 4,094,957, a rotation of the cylinder barrel, caused by the opening or closing of a sliding door, is converted in a translational motion of the piston. In contrast to the damper disclosed in AT 393 004, the damping torque of this rotation damper is adjustable.
An important drawback of this rotation damper is that it is relatively leak-prone. In particular in outdoor applications, which, to prevent being substantially affected by temperature changes, normally use a hydraulic fluid of low, substantially constant viscosity (i.e. a viscostatic fluid), the low viscosity of the fluid requests additional measures to prevent leaks. The fact that the cylinder barrel of this damper of the prior art presents openings at both ends increases the risk of leaks, facilitated both by gravity, and by the higher pressures on the second side of the cylinder cavity. In the first, low pressure side of the cylinder cavity, the damper shaft is more particularly sealed by means of a shaft seal in an opening in a lid closing the top of the cylinder barrel. Due to the fact that the rotation damper is disposed horizontally, the hydraulic fluid can constantly leak by gravity along this shaft seal. In the second, high pressure side of the cylinder cavity the cylinder barrel is provided with an opening for a damping adjustment needle valve. This opening is sealed with a shaft seal around the needle of the needle valve. Hydraulic fluid cannot only leak by gravity along this shaft seal but especially also by the high hydraulic pressure which may be generated in the second side of the cylinder cavity. Although only very small amounts of hydraulic fluid may leak out of the damper, it is important to avoid even such small leaks since the damper should be maintenance free for a large number of years.
It is a first object of the present invention to provide an adjustable hydraulic damper which is nevertheless substantially leak-free.